1. Field of the Invention
The present invention relates to a roller member and a method of producing the same, and in particular a roller member such as a roller cam follower use to a cam apparatus for turning a locker arm in a valve system of, for example, a car engine and a method of producing the same.
2. Field of the Invention
For instance, in the cam apparatus for turning the locker arm in the valve system of the car engine, a lubricating oil is insufficiently supplied to a contact between the cam and the roller cam follower, so that lubricating conditions are severe, and besides since the roller cam follower performs to the cam not a purely rolling contact but a rolling contact bringing with slide, the roller cam follower is ready for causing peeling in an outer circumference as a rolling face in a short period of time, resulting to shorten a service life.
Then, an assignee of this invention proposed, aiming at lengthening a life, a roller cam follower (Patent Laid Open No. 7-54616) comprising a blister steel (case hardened steel), performed with a carburization treatment, having a surface hardness of 63 to 68 in Rockwell C hardness (called as “HRC” hereafter), and containing surface residual austenite of 13 to 30 vol %. A reason for determining the surface hardness to be HRC 63 to 68, is because to avoid damages becoming a peel starting point when biting foreign materials or worsening the lubricating conditions as well as to secure toughness. Further, a reason for determining the surface residual austenite to be 13 to 30 vol % is because to prevent toughness from lowering to avoid cracking progressing, and check dimensional changes owing to martensite deformation when heating.
However, the above mentioned existing roller cam follower scarcely has carbides on the surface, and abrasion resistance is not satisfactory. As a raw material, the case hardened steel is employed. Since the case hardened steel is not mass-produced, a material cost is high, and as a result of heat treating costs for the carburization treatment or a carbonitriding treatment of the case hardened steel are expensive, a problem is to heighten total production cost of the roller cam follower.
It is therefore considered to carry out the carburization treatment or the carbonitriding treatment on a worked blank of the roller member formed into a predetermined shape from the bearing steel (high carbon chromium bearing steels) such as JIS SUJ2 for producing the roller cam follower, but in this case, it is not possible to concurrently increase surface hardness and refine carbides, and for example, if the carburization treatment is carried out on JIS SUJ2 inherently containing high carbon and carbide in order to increase the surface hardness, the already existing carbide more grows to be gigantic, and after all the service life is shortened.
Accordingly, it is an object of the invention to offer a roller member having a longer life than that of the conventional one and a method thereof.